SHALLOW HYDROGEOLOGICAL AND HYDROCHEMICAL CHARACTERIZATION OF THE AQUISTORE CO2 SEQUESTRATION SITE IN ESTEVAN, SASKATCHEWAN, CANADA

Aquistore is a carbon capture and storage project with the purpose of post-combustion capture of CO₂ from a coal-fired electrical generating station in Estevan, Saskatchewan, Canada. Carbon dioxide will be geologically sequestered in deep brine formations at the Aquistore site. One component of the measurement, monitoring, and verification (MMV) program developed to minimize risks associated with potential leakage was the characterization of shallow hydrogeology. Baseline hydrogeological and hydrochemical data are critical for demonstrating that injected CO₂ has not migrated into overlying shallow aquifers and altered the quality of groundwater resources. Thus, in order to establish the hydrogeological properties of the site, physical and chemical data were collected from a network of newly-installed and existing groundwater wells.

The focus area of the groundwater monitoring program was determined to be a 3-km radius of the site, based on the projected extent of the CO₂ plume after 10 years of CO₂ injection. Three major monitoring events were completed prior to CO₂ injection: Spring 2013, Fall 2013, and Spring/Summer 2014. A total of 40 wells were monitored and sampled, with field measurements including depth to water level, pH, conductivity, and temperature. Samples were collected and analyzed for a suite of chemical parameters including major and minor elements and compounds, dissolved organic (DOC) and inorganic carbon (DIC), and stable isotopes. Geochemical results revealed a wide variety of chemical compositions but were generally found to be consistent over time, with little seasonal variation. Water levels were measured during the discrete geochemical sampling events; these data combined with eleven pressure transducers installed in selected wells were used to determine horizontal and vertical groundwater flow directions at the site. Analysis of the measured pressure data collected over time was used to understand natural temporal variations in groundwater levels in the area.

Once CO₂ injection commences, shallow groundwater monitoring will serve as an integral part of Aquistore’s MMV program by providing a framework in which hydrogeological changes, and thus CO₂ intrusion, can be assessed.